dht: pass xdata to xlators above.

Change-Id: I96e9feb88443fcd7da40c33c0e8c4e2645b1fcf3
BUG: 1096047
Signed-off-by: Krishnan Parthasarathi <kparthas@redhat.com>
Reviewed-on: http://review.gluster.org/7872
Reviewed-by: Shyamsundar Ranganathan <srangana@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>